Field of the Invention
The invention relates to a control device and to a method for controlling a hydraulic pressure of a fluid transmission and use thereof.
Hydraulic open-loop and closed-loop pressure controllers are used, inter alia, in many applications for vehicles, in particular in automatic transmissions. Automatic transmissions frequently have electronic control devices which are configured to generate electrical signals and with the latter to actuate solenoid valves to control an oil flow or pressure.
Many methods for actuating hydraulic solenoid valves in the field of automobile transmissions use what are referred to as open-loop algorithms. Open-loop algorithms have many advantages. They are low in cost because, for example, no pressure sensor is required. Because of the lower expenditure on conditioning signals, the computing capacity requirement of microcontrollers which are used for them is relatively low. Furthermore, the development costs of the software are also low.
However, open-loop algorithms also have deficiencies. The operating conditions for a transmission change in the course of time, since the transmission components age and become worn out. Clutches which are operated with hydraulic oil are the most frequently used actuators of a power train. The properties of clutch springs and clutch plates change in the course of time. Moreover, the properties of the transmission oils change in the course of time owing to soiling and aging.
Open-loop algorithms are not adapted to such changes, for example changes in calibration which occur in the course of time, and are, in particular, not suitable for compensating changes in properties of a system over its entire service life.
Owing to these deficiencies of open-loop algorithms, what are referred to as closed-loop control algorithms are alternatively used in the field of transmission control. In a closed-loop system, a pressure sensor is necessary to supply a feedback signal (actual signal).